Inorganic 2D Materials for Selective Separation Membranes

拟议的项目旨在研究使用各种2D材料形成膜，这些膜可以作为各种分子和离子种类的选择性和可调分离器。这种膜的潜在应用是巨大的，并且包括：水过滤（例如海水脱盐和在环境修复中去除重金属、有毒有机污染物、放射性元素），非水过滤（例如催化剂回收、溶剂再循环、离子液体等），甚至是能量产生（例如氧化还原液流电池和渗透能）。这些膜将由主要无机材料的广泛库构成;包括过渡金属二硫属化物（例如MoS 2、WS 2、MoSe 2、WSe 2等），六方氮化硼（hBN）和层状金属氧化物（例如V2 O 5、MoO 3、WO 3）。这些2D材料中的每一种都可以从块状形式剥离到单个或几个分层厚薄片的分散体。然后，这些分散体可用于产生由所需2D材料的堆叠层组成的“纸”状膜。与单组分膜一样，将进行复合膜的形成，其由多种不同的分层2D材料组成，允许我们调整所需的过滤性能。目前的过滤技术需要使用能量效率极低的膜，其需要大量的能量来实现所需的溶剂通量以及对不需要的物质的可接受的排斥。在用于脱盐或纯化的水反渗透的情况下，通常使用基于聚合物的膜。为了实现过滤水的期望通量，必须施加非常大的施加压力以迫使水通过，同时排斥溶解的离子（例如Na+、Cl-）。这需要大量的电力，而且效率极低。由于由2D材料组成的膜的固有特性，它们可以克服这一缺点，并允许大大提高水过滤效率，同时通过所产生的化学势梯度产生能量。这是通过在2D晶体的相邻层之间形成溶剂分子的纳米胶囊来实现的。这允许溶剂分子的极其有效的输送，但非常高地排斥不能适合毛细管通道的不期望的水合离子。基于2D材料的膜在剥离晶体层之间的间距中的定义特征，因为这决定了允许的物质的尺寸是多少。目前，人们对使用石墨烯和氧化石墨烯（GO）基材料用作分离膜，特别是用于水过滤的分离膜非常感兴趣。这是由结果所推动的，这些结果表明，基于GO的膜表现出极高的水传输，同时拒绝较大的分子种类，使它们成为可能的过滤应用的理想选择。然而，尽管这些GO膜有希望，但到目前为止仍有几个关键问题阻碍了进一步的进展。这包括当使用实际过滤固有的高压时的长期稳定性和机械强度的问题。令人惊讶的是，大量类似结构的无机2D材料的使用仍然几乎没有触及，只有少数现有的研究表明，这些其他材料显示出巨大的前景，具有高溶剂通量以及优异的截留性能。选择无机2D材料以及石墨烯的复合材料的使用将允许它们彼此互补以从给定溶剂中选择性地去除所需物质。

The proposed project aims to investigate the use of a variety of 2D materials for the formation of membranes that can function as selective and tuneable separators for a wide variety of molecular and ionic species. The potential applications of such membranes are vast and include; water filtration (e.g. sea water desalination and the removal of heavy metals, toxic organic contaminants, radioactive elements in environmental remediation), non-aqueous filtration (e.g. catalyst recovery, solvent recycling, ionic liquids etc.), and even energy generation (e.g. redox flow batteries and osmotic power). These membranes will be constructed from a wide library of predominantly inorganic materials; including transition metal dichalcogenides (e.g. MoS2, WS2, MoSe2, WSe2, etc.), hexagonal boron nitride (hBN), and layered metal oxides (e.g. V2O5, MoO3, WO3). Each of these 2D materials can be exfoliated from a bulk form down to a dispersion of individual or few layered thick flakes. These dispersions can then be used to create 'paper' like membranes consisting of stacked layers of the desired 2D material. As well as single component membranes the formation of composite membranes will be performed which consist of a plurality of various different layered 2D materials, allowing us to tune the desired filtration properties. Current filtration technology requires the use of extremely energy inefficient membranes which require enormous amounts of energy to achieve the desired solvent flux combined with acceptable rejection of the unwanted species. In the case of water reverse osmosis for desalination or purification a polymer based membranes is typically used. To achieve the desired flux of filtered water very large applied pressures must be applied to force the water through while rejecting the dissolved ions (e.g. Na+, Cl-). This requires very large amounts of electricity and is highly inefficient. Due to the intrinsic properties of membranes consisting of 2D materials they can overcome this drawback and allow for vastly increased efficiency of water filtration, as well as simultaneously generating energy through the created chemical potential gradient. This is achieved through the formation of nanocapillaries of solvent molecules which are formed in between the neighbouring layers of 2D crystal. This allows for extremely efficient transport of solvent molecules but very high rejection of undesired hydrated ions which cannot fit into the capillary channels. The defining feature of 2D material based membranes in the spacing between the layers of exfoliated crystal as this determines what the size of allowed species is.There is currently a great deal of interest in the use of graphene, and graphene oxide (GO), based materials for use as separation membranes, particularly for water filtration. This is fuelled by results which show that GO-based membranes exhibit extremely high water transport while rejecting larger molecular species making them ideal for possible filtration applications. However, despite the promise of these GO membranes there are several key issues which have so far prevented further progress. This includes issues with long term stability and mechanical strength when high pressures inherent to practical filtration are used. Surprisingly, the use of the vast number of similarly structured inorganic 2D materials remains barely touched with only a handful of existing studies that indicate that these other materials show immense promise with high solvent flux as well as excellent rejection properties. The use of composites of both a selection of inorganic 2D materials as well as graphene would allow them to complement one another to selectively remove desired species from a given solvent.